Start a new RTG with an existing player. Choose a good QB that is a starter. I used Mizzou"s QB. Make sure to put the difficulty on freshman.
Play the practice first. You should be able to earn the 1000 points it takes to level up your coach trust. You cannot earn any more points after leveling up in a game or practice.
After the practice for that week play the game. Always skip till you are on the field with X. If the play is a run play you can skip that too. After 3 or 4 TD's passes you should have your 1000 to level up your coach trust. I had enough points by halftime every game. When you do super sim to the end of the game since you cant earn anymore points.
Do this for 3-4 weeks and when you get max coach trust the achievement will pop when you advance the week (or at least when mine did)
***NOTE***
I earned all of my other RTG achievements with a RB and I decided it was gonna take too long to earn max trust that way. I bought the max coach trust off the marketplace. The achievement would not unlock after that. So i deleted it and tried this method. Took about 30 mins